Performance and stability of schottky barrier mixers

We discuss the performance of a Schottky barrier diode as a mixer when the barrier of the diode is open-circuited at the harmonics 2ω
o
, 3ω
o
, etc. of the pump frequency ω
o
. Such a mixer is shown to be capable of arbitrarily high conversion gain provided
$\omega_{c} \geqq \eta\omega_{o},$
where ω
c
, is the cutoff frequency of the diode and η is a parameter that is typically less than 6.25 and approaches 4 under certain ideal conditions. It is shown that the limit imposed by the series resistance of the diode on the double-sideband noise figure of the mixer is given by
$F_{m} > \left(1 - \eta {\omega_{o} \over \omega_{c}\right)^{-1}.$
An experiment is described at 1.25 GHz on a room temperature mixer whose double-sideband noise figure F
m
as a function of gain has a minimum of about 0.7 dB (for gain less than unity) and a maximum of about 2.3 dB (for high gain).